Refractories and bonding agents therefor



July 27, 1954 R. R. WEST y2,684,913

REFRAcToRIEs AND BONDING AGENTS THEREFOR Filed Jan. 6. 1951 S L2 QQ, g iv 4 b: 9 S N) w E g n Ua g a Q h w Hs 4 '217/ A /gf/ wf/ 7g(Ay/101400040; 7l/W'1 INVENroR.

Patented `Iuly 27, 1954 REFRACTORIES AND BONDING AGENTS THEREFOR RichardR. West, Alfred, N. Y., assignor to North American Cement Corporation,Catskill, N. Y., a corporation of Delaware Application January 6, 1951,Serial No. 204,790

(Cl. G-64) 8 Claims.

This invention relates to refractories and to bonding agents for suchrefractories.

It has long been recognized that hydraulic bonding agents such ascalcium silicate-Em constitute excellent but r''le i'veIy inexpensivebonding agents for a variety of aggregates and that they serveparticularly well as bonding agents for structural concrete. It has alsobeen recognized that hydraulic cements such as calcium silicate cementsand more particularly various Pori-,lang gements upon being heated toelevated emperatures and then cooled have a tend- 4 ency to firstdehydrate and then rehydrate. This characteristic has placed severelimitations upon the utilization of such hydraulic bonding agents in theproduction of refractories. It has further been recognized that calciumsilicate cements have the disadvantage of being subjected to mineralinversion and resulting expansion at the elevated temperatures now oftenexperienced in refractory furnaces and that this characteristic ofcalcium silicate cements likewise limits their utilization for bondingrefractories. Up to the present time, no known practicable solutions tothe stated problem have been oiered. As a result, stable refractoriescontaining conventional calcium silicate cements as the principal orsole bonding agent which can be subjected to varied elevatedtemperatures, say, up to and including temperatures of 3000 F., and evenabove are not available.

It is an object of this invention to provide a calcium silicate bondingcomposition for refractories which may be used to form a stable bond forrefractories at the higher service temperatures now encountered.

It is a special object of this invention to provide calcium silicatebonding compositions stable at high and low temperatures and stable towide temperature variations, including both heating and coolingtemperatures.

It is another object of this invention to provide stable and inexpensivecastable refractories.

It is an additional object of this invention to provide a castableconcrete mix composed substantially completely of calcium silicate,Which, when formed into a concrete, constitutes a refractory stable overa wide range of service temperatures.

It is still another object of my invention to provide both acid andbasic castable refractories having exceptional refractoriness and otherimproved properties.

Other objectives and purposes of my invention will appear from the moredetailed description which follows.

I have found that a superior hydraulic bonding agent for refractoriesmeeting the objectives of my invention can be produced from c lciumsilicate cements by adding to such cements stabilizing quantities ofcarbonaceous materials which form oxides of carbon at 10W temperatur? ana so y a 1 1 izing quantities of substantially wate vs c o; veiuclnripjQ unnlgl's, Such cemen 1 1ous bonds are sta e in tories subject toservice temperatures as high as 3000 F. Where Portland cement clinker isused as an aggregate and service temperatures in excess of 1800 F. areexperienced in the use of the refractories, it has been found necessaryto add lglor its equivalent as a stabilizing agent for the calcium oxideformed in the cementi ious bonds at such temperatures. Where otherconventional refractory aggregates are used oxides are usually presentin a suicient quantity to bind the oxide of calcium formed attemperatures above 1800 F. Casta-ble refractories stable at servicetemperatures as high as 2200 F. can be bonded with calcium silicatecements containing stabilizing quantities of carbonaceous material.

It is Well known that most of the refractories are now made of varioustypes of refractory brick. even though castable refractories have knowndecided advantages over such refractories. 'Ihis preference forpre-formed refractories is mainly attributable to the superiorrefractoriness of such materials. At the present time castablerefractory aggregates consist either of ground re brick, ground calcinedfire clayl ground high alumina materia s inc uding ground hi h-aluminaErick, n or fused material. For example, at the present time ere 1s noacid castable suitable for replacing silica refractories, and there areno basic castables capable of replacing basic brick refractories. Thefailure to provide refractory castables stable to high servicetemperatures is due to the fact that calcium aluminate cementsheretofore used in forming refractories subjected to high servicetemperatures have extremely low fusion temperatures in the presence ofsuch acid or basic materials. As the result of my discovery, I have nowprovided castable refractories containing basic agg gg g tes such asfired cement clinkers or aci U e ates such as re brick or high aluminabrick having superior refractoriness and other improved properties, suchas stability to heating and cooling.

A castable refractory can be used to advantage to replace loose dolomiteor magnesite clinker that is now used for a monolithic hearth in thebasic open hearth furnace. Such castable presents a more impenetrablesurface to the attack of molten metal than does the present looseclinker installation. There are many other applications that arise wherea basic castable might be desirable if the fusion temperature issufficiently high to allow a suiliciently high service temperature.

Due to the fluidity of castable refractories, much time and skilledlabor is saved by casting them at the place where they are used.Castable refractories are versatile in methods of applica- 1 tion asthey may be puddled into forms in a manner similar to the way concreteis used. They may be rammed into forms or molds using a comparativelydry mixture with water by hand hammering or an air hammer. They may beapplied by cement-gun methods in which the dry material is blown througha nozzle at which time mis added to the mixture thus making it stick toa wall. The latter method is used extensively for castable linings ofstacks or chimneys and in patching refractory walls.

In the production of my novel castable refractoi'ies I may use from 95to 50% by weight of the refractor a g and from about 5 to 50% by weightof the calcium silicate bonding 25 agent. In general, I prefer toencompass a major proportion of the refractory aggregate in my castablesand generally use approximately 60% to 90% by weight of the aggregate.An especially valuable castable refractory is obtained by using about70% by weight of burned Portland cement clinker containing about equalquantities of clinker crushed to a neness of 8-30 mesh containing aminimum of nes, together with uncrushed clinker of conventional size, i.e. varying from 3A to 1A," in diameter.

The stabilizing agents used in my calcium silicate bonding compositionsmay be varied over a considerable range, depending, in part at least, onthe amount of aggregate used and on the service temperaturesencountered. The ncarbon material used to stabilize the cement'again'st`dehydration and rehydration at service temperatures up to approximately1800 F. is present in a quantity by Weight providing carbon in apercentage varying from about 0.4% to 20 based upon the amount ofcalcium silicate cement used. Boron compounds are usually present in aquantity by weight delivering B203 in a percentage varying from about0.02% to about 4% based upon the quantity of calcium silicate cementpresent. The finely ground clayV when necessary in my composition ispresent 1n a quantity varying from about 4% to about 60% by weight basedupon the weight of the calcium silicate cement present. Higherpercentages of clay usually lower the refractoriness of the cement to apoint Where it is no longer useful.

A typical class of calcium silicate bonding compositions of my inventionwould contain the following parts by weight:

Parts Pulverized Portland cement clinker 25 Carbon material (added inquantities 55 to give the following parts by weight of carbon 0.1 to 5Boron-containing substance (added in water-insoluble form in quantitiesto give the following parts by weight of BzO3) 0.005 to 1 Anothertypical class of calcium silicate bonding compositions would contain thefollowing parts by weight:

Y Parts Pulverized Portland cement clinker 25 Carbon material (added inquantities to give the following parts by weight of carbon) 0.1 to 5Boron-containing substance (added in water-insoluble form in quantitiesto give the following parts by weight of B203) 0.005 to 1 Finely groundclay 1 to 15 advantageously ground to a specific surface area of 1200 to2200 sq. cm. surface area per gram. Either type I or t e II Portlandcement clinker as described 1n American Society of Testing MaterialsDesignation 0150-49 which has been hardburned is most useful for formingmy calcium silicate type cement. Other types of Portland cement, namely,t es III ay be used to somewhat less advantage. Other types of .calciumsilicate cements such as Portlandblast furnace slag cement, pozzuolancement,

true pozzuolanic cement, slag cement, and naura cemen may also be used1n my calcium silicate Bonding compositions, but they have no advantagesover the more economical pulverized Portland cement clinker.

The Portland cement clinker used as a refractory aggregate may be any ofthe types previously described. Type I and type II which have been hardburned are also preferred as aggregates.

A mixture of about 30 parts by weight of gngound Portland cement clinkerranging from 3/4 tg" in diameter combined with about 38 parts ofPortland cement clinker ground to from 8 to 30 meshwen combined with mycalcium silicate bonding composition constituted a dense concrete mix ofsuperior properties.

Where it is desired to make a basic castable @fram-,plof unusually highrefractoriness, it is best to use various types of magnesite. A calcinedmagnesite ground to a fineness of 8 to 30 mesh with a minimum of nesthrough a 30- mesh screen is particularly advantageous. A typicalcommercial magnesite of this type is known by the designation ofChewelah magnesite. When using such magnesite as aggregates no advantagewas obtained by using a mixture of ground and unground materials. Othermagnesites may be used with equal advantage as aggregates, such as fusedmagnesite or periclase, but such materials are usually uneconomicil.Other known basic refractory aggregates heretofore used, such asdolomitic clinker, chromite, and ground basic brick may likewise be usedin place of the calcine magnesite with substantially equal results.

The carbon material used in my bonding compositions and refractories maybe any carbona- 7 or carbon dioxide on heating to temperatures up to1800 F. Under such conditions the oxides of carbon are believed tocombine with the calcium oxide formed on dehydration forming calciumcarbonate, which does not rehydrate when the refractory is cooled.Preferred materials oxidize insoluble boron compounds are shown attemperatures above 242 F. but below 800 F. Various types of lamp blacksor carbon blacks such as are used or 1CT .and in the rubber industryhave been found advantageous since they may be easily and thoroughlydispersed in the cementitious bond. Certain types of lamp black havesuperior stabilizing properties. Gra hite either in crystalline oramorphous form, and coal or commayasobm carbonaceous material should notbe used in a quantity which will weaken the structure of the refractorythrough the formation of excessive porosity. The foregoing carbonaceousmaterials all contain carbon in a chemically uncombined state, and itwill be understood that "carbonaceous material or carbonaceoussubstance, as used herein, refers to materials or substances containingcarbon in a chemically uncombined state. In the compositions of myinvention, it is only necessary to use boron compounds in a quantitywhich prevents man of the dicalciums e rom e a o egamma crm. I 1s nei ernecessary nor advantageous to have the boron compound present in aquantity which through fusion forms a vitreous bond at temperaturessubstantially lower than those often experienced in modern refractories.Substantially found Suitable may be in amorphous 0r glass s ate. Theboron compoundsused 1n my compositions must be substantially insolublein water and in the concrete mixes in order that the presence of suchcompounds not impair the set or strength of the refractories. Suchmaterials as Pyrex glass containing 13% or more of B203 and other maerials with varying percentages of B203 which are water-insoluble may beused. Crystalline compounds such as CaO.B2O3 2CaO.B2O3, 3CaO.B2O3,5CaO.B2O3.SiO2, CaO.B2O3.2SiO2 may be used. Other substantiallywater-insoluble compounds providing boron at temperatures above 1800 F.known commercially may be used. Water-insoluble boron compoundscontaining from 20% to 40% B203 not only prevented mineral inversion,but also had little or not effect on the set of the cement. Typicalcommercially available waterereinbelow. Frits manufactured by the FerroEnamel Com- Frit manufactured by Pemco Corporation, Eastern and PemcoAvenues, Baltimore, Maryland,

Lithium carbonate 15 The oxides needed to react lwith lime formed in mycem 1 lous on ng agents at emperatures above 1800 may be provided andare generally provided in conventional refractory ag- 5 gregates. Wherefired Portland cement clinkers are used as aggregates it is necessary toadd oxides which react with lime formed at the stated highertemperatures. Finely ground clay is inexpensive and serves well to bindany lhmmed 10 since the oxides of such clays begin to react with calciumoxide at temperatures as low as 1500u F. Other finely divided refractorymaterial containing oxides reactive with calcium oxide which may readilybe dispersed in the calcium silicate cement composition may be usedalso.

The following examples in which the parts are expressed as parts byweight constitute illustrative embodiments of my invention.

EXAMPLE 1 Parts by weight Pulverized calcium silicate type cement clnkerCarbon material (added to give the following parts by weight of carbon)1 25 Boron-containing substance (introduced in a water insoluble form togive the following parts by weight of B203) 0.04

The bonding agent of this example can be used to produce a refractorycastable which is stable at 3009;5. A typical castable refractory wouldcontain one part of the bondinngnagent of this example with 2 to 4 partsof an ,axgqgregxatfsuch as calcined magnesite or ground maenesnlt brick.Such a refractory castable has a fusion point well over 3000 F. Where achemically basic character is important in the refractory material,other basic materials such as forsterite, chromite. stabuizeg dolomiti@aunkenmas-rae used in place of the magnesite.

EXAMPLE 2 Parts by weight Pulverized calcium silicate type cement 4clinker 25 Carbon material (added to give the following parts by Weightof carbon) 1 Boron-containing substance (introduced in a water insolubleform to give the follow- 5 ing parts by weight of B203) 0.04 Finelyground clay 5 'Ihe bonding agent of this example may be used with acalcium silicate clinker as an aggregate and yet remain stable at hlglservice temperatures. Typical refractory castable compositions wouldcontain one part of the calcium silicate bonding agent of this examplewith two to three parts by weight of Portland cement clinler;

EXAMPLE 3 Per cent Pulverized Portland cement clinker 25 Globe Black* 1Borate Frit 3195 (Ferro Enamel Co.) 1 Calcined Chewelah magnesite 73 A.1am black manufactured by the L. Martin Company,

Inc., 4 s reet, New York 17, N. Y.

This example constitutes a typical basic refractory stable atexceptionally high service temperatures. For instance, the castablerefractory of this example has a pyrometric cone equivalent (PCE) abovecone 30 which represents a service temperature of at least 3002 F.Additionally, a cast refractory material made from the refractorycastable of this example is not attacked by basic slag such as Portlandcement @ker when in contact with it at te'atures" EXAMPLE 4 Per centPulverized Portland cement clinker 2:?sa gil25 EXAMPLE 5 Per cent byweight 'Iype III Portland cement 25 5 Finely ground clay 5 3195 boratefrit 1 Globe Black 1 8-30 mesh Portland cement clinker 38 UngroundPortland cement clinker 30 l0 The castable of this example was used tomanufacture experimental preformed chimney blocks and cast maple sugarhearths. The experimental installations have operated over a sufcientlylong period of time to demonstrate Globe Black 1 15 the practicalutility of such cast materials.

Borate Frit 3195 (Ferro Enamel Co.) 1 EXAMPLE 6 Finely ground clay "K'n" 5 Percent by Weight Portland Cement clmker"" iii?" 68 (Pulverizedtype I hard-burned Portland ce- Substantial advantages flow from thLe'fct that the aggregate and the bond used in this castable are t e same.The cast refractory material made mompositions of this inventionpossessed high strength and exceptionally fine thermal insulatingproperties. The superior insulating properties of refractory materialmade from the composition of this example are illustrated in theaccompanying graph. In the graph the thermal insulating properties of acast refractory made from-the compositions of this example are comparedwith light-weight insulating refractories of much less strength whichhave heretofore been considered necessary to produce refractories ofgood insulating qualities. In the graph the mean temperatures areplotted along the abscissa and the thermal conductivity (K) expressed inB. t. u.s per hour per square foot of area per degree F. of temperaturevariation per inch of thickness of the refractory is plotted along theordinate. In the graph, line anrepresents' the thermal conductivity of arefractory castable made from ground fire brick and bonded together witha calcium aluminate (Luminite) cement. Lineb`'prs`l`ts`tl`t'h`l'ductivity ofFaT-tnical insulating refractory madefrom ground insulating refractory brick bound together with a calciumailugmintecemggt. Line ,c represents thlcoductivity of afinsulatingrefractory brick stable at 2800 F. also bonded With a Calclllumae Eell:Line Y d represents th'tlfernal con/dutviiiyor inslilt'- `ing propertiesof a cast refractory made from the composition of ehxawmplem..

Cast refractory materials made from the compositions of this examplecontaining the stabilizing agents Globe Black, Borate Frit 3195, andnely ground clay were compared also with cast refractories notcontaining such ingredients. Cast test samples made with the castablewithout the stabilizing agents disintegrated after heating to 2300 F.and then cooling to room temperatures. Such disintegration apparently isdue to hydration of the lime in contact with the moisture of the air.Like samples of the castable refractory without the stabilizing agentsdisintegrated to a ne powder when heated above 2300 F. and then cooledbelow 1250 F. The powdering of the cast product not containing thestabilizing agents is believed to be attributable to the mineralinversion of the dicalcium silicate content of the cement. Cast samplesmade from the castables of this example remained stable under identicalconditions to those just described.

ment clinker 25 Finely ground clay 5 3195 borate frit 1 Globe Black 18-30 mesh Portland cement clinker 38 @Inground Portland cement clinker30 EXAMPLE 7 Percent by weight Pulverized type II hard-burned Portlandcement clinker 25 Finely ground clay 5 3195 borate frit l Globe Black l8-30 mesh Portland cement clinker 38 Inground Portland cement clinker 30The castables of the two foregoing examples have been usedexperimentally as iiue blocks in a clamp kiln for firing buildingbricks, as carburetor covers for water gas generators, as a wall sectionof the ash hopper of an oil-red steam boiler, and as a complete liningfor a ten foot laboratory rotary kiln. The experimental installationshave proven to be completely stable under the stated severe serviceevaluations.

EXAMPLE 8.REFRACTORY CASTABLE f Percent by weight Pulverized Portlandcement clinker 25 Globe Black (L. Martin Company) 1 Ground re brick 74EXAMPLE aREFRACT0RY CASTABLE Percent by weight Pulverized Portlandcement clinker 25 Globe Black (L. Martin Company) 1 5 Finely ground clay5 Portland cement clinker 69 The castables of the two preceding examplesare stable at service temperatures up to 2200 F. while similar productswithout the carbonaceous materials disintegrated after heating totemperatures of 2200 F., or even in some instances, after heating totemperatures as low as 800 F.

It will be apparent, also, that ground magnesite or chrome brick, groundcalcined iireclay, calcined magnesite or other aggregates common in themanufacture of refractory castables may be used instead of the Portlandcement aggregate or the ground nre brick.

It will be understood that the foregoing eX- amples constituteillustrative embodiments of my invention and that various modificationsand changes can be made therein without departing from the spirit of myinvention or the scope of the appended claims.

I claim:

1. A heat stable hydraulic bonding composition comprising a calciumsilicate cement stabilized by a carbon material present in a quantity byWeight varying from about 0.4 to 20% of said cement, and by a quantityof a substantially Water-insoluble boron-containing substance present ina quantity delivering B203 in an amount by Weight equal to at least0.02% of said cement but delivering B202 in a quantity insufficient toform a vitreous bond with refractory aggregates.

2. A heat stable hydraulic bonding composition comprising a calciumsilicate cement stabilized by a carbon material present in a quantity byweight varying from about 0.4 to 20% of said cement, by a quantity of asubstantially waterinsoluble boron-containing substance present in aquantity delivering B202 in an amount by Weight equal to at least 0.02%of said cement but delivering B202 in a quantity insufcient to form avitreous bond with refractory aggregates, and by clay present in aquantity by weight varying from about 4 to 60% of said cement.

3. A heat stable hydraulic bonding composition comprising Portlandcement ground to a surface area of about 1200 to 2200 square centimetersof surface area per gram stabilized by the presence of a carbon materialpresent in a quantity by Weight varying from about 0.4 to

20% of said cement, and by a quantity of a subf stantiallywater-insoluble boron-containing substance present in a quantitydelivering B202 in an amount by weight equal to at least 0.02% of saidcement but delivering B203 in a quantity insufficient to form a vitreousbond with refractory aggregates.

4. A stable refractory castable composition comprising a basicrefractory aggregate and a hydraulically hardenable bonding compositiontherefor comprising a calcium silicate cement stabilized by a carbonmaterial present in a quantity by weight varying from about 0.4 to 20%of said cement, and by a quantity of a substantially Water-insolubleboron-containing substance present in a quantity delivering B202 in anamount by weight equal to at least 0.02% of said cement but deliveringB202 in a quantity insuicient to form a vitreous bond with saidaggregate.

5. A stable refractory castable composition comprising an acidrefractory aggregate and a hydraulically hardenable bonding compositiontherefor comprising a calcium silicate cement stabilized by a carbonmaterial present in a quantity by weight varying from about 0.4 to 20 ofsaid cement, and by a quantity of a substantially water-insolubleboron-containing substance present in a quantity delivering B202 in anamount by weight equal to at least 0.02% of said cement but deliveringB203 in a quantity insumcient to form a. vitreous bond with saidaggregate.

6. A castable refractory composition comprising a Portland cementclinker aggregate and a hydraulically hardenable bonding compositiontherefor comprising a calcium silicate cement stabilized by a carbonmaterial present in a quantity by Weight varying from about 0.4 to 20 ofsaid cement, and by a quantity of a substantially water-insolubleboron-containing substance present in a quantity delivering B202 in anamount by Weight equal to at least 0.02% of said cement but deliveringB202 in a quantity insufficient to form a vitreous bond with saidaggregate.

7. A stable castable refractory composition comprising a Portland cementclinker aggregate composed of approximately equal quantities of ungroundPortland cement clinker and Portland cement clinker ground to a finenessof 8-30 mesh, and a hydraulically hardenable bonding compositiontherefor comprising a calcium silicate cement stabilized by a carbonmaterial present in a quantity by weight varying from about 0.4 to 20%of said cement, by a quantity of a substantially water-insolubleboron-containing substance present in a quantity delivering B203 in anamount by weight equal to at least 0.02% of said cement but deliveringB203 in a quantity insufficient to form a vitreous bond with saidaggregate, and by clay present in a quantity by weight varying fromabout 4 to 60% of said cement.

8. A refractory material comprising a refractory aggregate bondedtogether by a hydraulically hardened Portland cement stabilized by acarbon material present in a quantity by weight varying from about 0.4to 20% of said cement, and by a quantity of a substantiallywater-insoluble boroncontaining substance present in a quantitydelivering B203 in an amount by Weight equal to at least 0.02% of saidcement but delivering B20-2 in a quantity insuicient to form a vitreousbond With said aggregate.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 43,548 Held July 12, 1864 112,929 Kreischer Mar. 2l, 18711,852,595 Steinour Apr. 5, 1932 1,867,641 Witty July 19, 1932 2,083,180Work June 8, 1937 FOREIGN PATENTS Number Country Date 5,033 GreatBritain 1881 21,997 Great Britain 1891 4,632 Great Britain 1894 4,298Great Britain 1902 28,731 Great Britain 1903 10,792 Switzerland 1895

1. A HEAT STABLE HYDRAULIC BONDING COMPOSITION COMPRISING A CALCIUMSILICATE CEMENT STABILIZED BY A CARBON MATERIAL PRESENT IN A QUANTITY BYWEIGHT VARYING FROM ABOUT 0.4 TO 20% OF SAID CEMENT, AND BY A QUANTITYOF A SUBSTANTIALLY WATER-INSOLUBLE BORON-CONTAINING SUBSTANCES PRESENTIN A QUANTITY DELIVERING B2O3 IN AN AMOUNT BY WEIGHT EQUAL TO AT LEAST0.02% OF SAID CEMENT BUT DELIVERING B2O3 IN A QUANTITY INSUFFICIENT TOFORM A VITREOUS BOND WITH REFRACTORY AGGREGATES.